Double-bearing position encoder

ABSTRACT

A double-bearing position encoder has an axle stabilized within a housing via two bearings disposed on opposite walls of the housing. The axle is in communications with a rotating cam. The cam actuates a pulser so as to generate an active pulse at a tissue site for analysis by an optical sensor. The axle rotates a slotted encoder wheel or a reflective encoder cylinder disposed within the housing so as to accurately determine the axle position and, hence, the active pulse frequency and phase.

PRIORITY CLAIM AND REFERENCE TO RELATED APPLICATIONS

The present application claims priority benefit under 35 U.S.C. §119(e)to U.S. Provisional Patent Application Ser. No. 61/847,307, filed Jul.17, 2013 titled Double-Bearing Position Encoder, which is herebyincorporated in its entirety by reference herein.

BACKGROUND OF THE INVENTION

Noninvasive physiological monitoring systems for measuring constituentsof circulating blood have advanced from basic pulse oximeters tomonitors capable of measuring abnormal and total hemoglobin among otherparameters. A basic pulse oximeter capable of measuring blood oxygensaturation typically includes an optical sensor, a monitor forprocessing sensor signals and displaying results and a cableelectrically interconnecting the sensor and the monitor. A pulseoximetry sensor typically has a red wavelength light emitting diode(LED), an infrared (IR) wavelength LED and a photodiode detector. TheLEDs and detector are attached to a patient tissue site, such as afinger. The cable transmits drive signals from the monitor to the LEDs,and the LEDs respond to the drive signals to transmit light into thetissue site. The detector generates a photoplethysmograph signalresponsive to the emitted light after attenuation by pulsatile bloodflow within the tissue site. The cable transmits the detector signal tothe monitor, which processes the signal to provide a numerical readoutof oxygen saturation (SpO₂) and pulse rate, along with an audible pulseindication of the person's pulse. The photoplethysmograph waveform mayalso be displayed.

Conventional pulse oximetry assumes that arterial blood is the onlypulsatile blood flow in the measurement site. During patient motion,venous blood also moves, which causes errors in conventional pulseoximetry. Advanced pulse oximetry processes the venous blood signal soas to report true arterial oxygen saturation and pulse rate underconditions of patient movement. Advanced pulse oximetry also functionsunder conditions of low perfusion (small signal amplitude), intenseambient light (artificial or sunlight) and electrosurgical instrumentinterference, which are scenarios where conventional pulse oximetrytends to fail.

Advanced pulse oximetry is described in at least U.S. Pat. Nos.6,770,028; 6,658,276; 6,157,850; 6,002,952; 5,769,785 and 5,758,644,which are assigned to Masimo Corporation (“Masimo”) of Irvine, Calif.and are incorporated in their entireties by reference herein.Corresponding low noise optical sensors are disclosed in at least U.S.Pat. Nos. 6,985,764; 6,813,511; 6,792,300; 6,256,523; 6,088,607;5,782,757 and 5,638,818, which are also assigned to Masimo and are alsoincorporated in their entireties by reference herein. Advanced pulseoximetry systems including Masimo SET® low noise optical sensors andread through motion pulse oximetry monitors for measuring SpO₂, pulserate (PR) and perfusion index (PI) are available from Masimo. Opticalsensors include any of Masimo LNOP®, LNCS®, SofTouch™ and Blue™ adhesiveor reusable sensors. Pulse oximetry monitors include any of MasimoRad-8®, Rad-5®, Rad®-5v or SatShare® monitors.

Advanced blood parameter measurement systems are described in at leastU.S. Pat. No. 7,647,083, filed Mar. 1, 2006, titled Multiple WavelengthSensor Equalization; U.S. Pat. No. 7,729,733, filed Mar. 1, 2006, titledConfigurable Physiological Measurement System; U.S. Pat. Pub. No.2006/0211925, filed Mar. 1, 2006, titled Physiological ParameterConfidence Measure and U.S. Pat. Pub. No. 2006/0238358, filed Mar. 1,2006, titled Noninvasive Multi-Parameter Patient Monitor, all assignedto Cercacor Laboratories, Inc., Irvine, Calif. (“Cercacor”) and allincorporated in their entireties by reference herein. An advancedparameter measurement system that includes acoustic monitoring isdescribed in U.S. Pat. Pub. No. 2010/0274099, filed Dec. 21, 2009,titled Acoustic Sensor Assembly, assigned to Masimo and incorporated inits entirety by reference herein.

Advanced blood parameter measurement systems include Masimo Rainbow®SET, which provides measurements in addition to SpO₂, such as totalhemoglobin (SpHb™), oxygen content (SpOC™), methemoglobin (SpMet®),carboxyhemoglobin (SpCO®) and PVI®. Advanced blood parameter sensorsinclude Masimo Rainbow® adhesive, ReSposable™ and reusable sensors.Advanced blood parameter monitors include Masimo Radical-7™, Rad-87™ andRad-57™ monitors, all available from Masimo. Advanced parametermeasurement systems may also include acoustic monitoring such asacoustic respiration rate (RRa™) using a Rainbow Acoustic Sensor™ andRad-87™ monitor, available from Masimo. Such advanced pulse oximeters,low noise sensors and advanced parameter systems have gained rapidacceptance in a wide variety of medical applications, including surgicalwards, intensive care and neonatal units, general wards, home care,physical training, and virtually all types of monitoring scenarios.

FIG. 1 illustrates an active pulse generator 100 that installs within areusable optical sensor for precisely pulsing a tissue site, such afingertip. The active pulse generator 100 has a motor 110, a cam 120, ahousing 130, a pulser 140 and an optical encoder 200. The cam 120 andpulser 140 are located within the housing 130. A shaft 160 couples themotor 110 to the cam 120 so as to linearly-actuate the pulser 140 uponapplication of electric current to the motor 110. The encoder 200extends into the housing 130 so as to mechanically couple to the cam120. The encoder 200 measures the rotation of the cam 120 and hence theposition of the pulser 140. Based upon encoder feedback, the pulser 140frequency and phase, and hence that of an active pulse, can beaccurately measured and controlled. An active pulse reusable opticalsensor is described in U.S. patent application Ser. No. 13/473,477,titled Personal Health Device, filed May 16, 2012 and assigned toCercacor is hereby incorporated in its entirety by reference herein.

FIG. 2 further illustrates the encoder 200, which has a housing 210, asingle-bearing 220 that mounts an encoder axle 230 to an encoder wheel240 and an optics assembly that senses reflective position tracks and anindex track on the encoder wheel 240 so as to generate a two-channelquadrature square wave output indicative of the axle 230 position.

SUMMARY OF THE INVENTION

A single-bearing encoder wheel mount, as described with respect to FIG.2, above, has insufficient mechanical stability to provide optimumaccuracy in measuring and controlling the phase and frequency of anoptical sensor active pulse. Double-bearing position encoder embodimentsadvantageously improve encoder wheel stability so as to improve activepulse accuracy and also solve encoder wheel/optical reader configurationissues created by the necessary location of the stabilizing secondbearing.

One aspect of a double-bearing position encoder is a housing, a pair ofbearings disposed within opposite facing walls of the housing and anaxle disposed within the housing and supported by the bearings. The axleis in mechanical communications with a pulser. An encoder wheel havingwheel slots is fixedly attached to the axle. An LED is disposed withinthe housing so as to illuminate the encoder wheel. A detector isresponsive to the LED illumination after optical interaction with thewheel slots as the axle rotates the wheel so as to indicate the wheelposition.

In an embodiment, the axle is stabilized within a housing via bearingsdisposed on opposite walls of the housing. The axle is in communicationswith a rotating cam that actuates a pulser so as to generate an activepulse at a tissue site for analysis by an optical sensor. The axlerotates a slotted encoder wheel or a reflective encoder cylinder so asto accurately determine the axle position and, hence, the active pulsefrequency and phase.

In various embodiment, the encoder comprisies an encoder mask havingmask slots disposed over an edge and along both sides of the encoderwheel so that the LED illumination passes through the mask slots and thewheel slots before reaching the detector. The encoder mask is folded sothat LED light is reflected off of the mask a first time beforeilluminating the encoder wheel and second time before reaching thedetector. Alternatively, the encoder mask is folded so that LED light isnot reflected off of the mask before illuminating the encoder wheel andbefore reaching the detector.

Another aspect of a double-bearing position encoder is a rotatable axle.An encoder wheel is rotatably mounted on the double-bearing-mountedaxle. An encoder mask is folded proximate an outer edge of the encoderwheel. Wheel slots are disposed around the encoder wheel proximate theouter edge. Mask slots are disposed through the encoder mask, and anemitter and a detector are disposed proximate to and on either side ofthe encoder wheel so that light intermittently passes through theencoder wheel via the wheel slots and the mask slots.

In various embodiments, light is reflected from the emitter off of themask at least once before it reaches the detector. Light is reflectedfrom the emitter off of the mask twice before it reaches the detector.The emitter directly illuminates the detector without reflection off themask.

A further aspect of a double-bearing position encoder is a doublebearing means of stabilizing a rotatable axle within an encoder housing.An encoder wheel means fixedly mounted to the axle so as to rotate asthe axle rotates. An illumination and detection means of intermittentlypassing light through the encoder wheel means as it rotates, and afolded and slotted mask means of precisely passing light through encoderwheel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective illustration of an optical sensor active pulsegenerator including a single-bearing position encoder;

FIG. 2 is a cutaway side view of a single-bearing position encoder;

FIGS. 3A-B are cutaway side views of double-bearing position encoderembodiments incorporating a slotted wheel encoder;

FIG. 4 is a cutaway side view of a double-bearing position encoderembodiment incorporating a reflective cylinder encoder;

FIGS. 5A-B are front and back perspective views of a double-bearingposition encoder assembly;

FIGS. 6A-B are partially exploded and exploded perspective views,respectively, of a double-bearing position encoder assembly;

FIGS. 7A-E are top, front, bottom, side and perspective views,respectively, of an encoder mask block;

FIGS. 8A-D are top, perspective, front and side views, respectively, ofan encoder mask;

FIGS. 9A-D are top, perspective, front and side views, respectively, ofa slotted encoder wheel;

FIGS. 10A-E are top, perspective, front, back and side views,respectively, of an encoder front housing;

FIGS. 11A-E are top, perspective, front, back and side views,respectively, of an encoder back housing;

FIGS. 12A-E are top, bottom, perspective, front and side views,respectively, of an encoder flex circuit;

FIGS. 13A-B are top and bottom exploded views, respectively, of flexcircuit optics and a corresponding encoder mask block;

FIGS. 14A-B are assembled and partially exploded perspective views,respectively, of another double-bearing position encoder assembly;

FIGS. 15A-D are front, perspective, top and side views, respectively, ofan encoder mask block;

FIGS. 16A-D are front, perspective, top and side views, respectively, ofan encoder mask;

FIGS. 17A-B are top and bottom exploded views, respectively, of flexcircuit optics and a corresponding encoder mask block;

FIGS. 18A-B are front and back perspective views of a furtherdouble-bearing position encoder assembly;

FIGS. 19A-B are top and bottom partially exploded perspective views,respectively, of a further double-bearing position encoder assembly;

FIGS. 20A-B are top mostly exploded and exploded perspective views,respectively, of a further double-bearing position encoder assembly;

FIGS. 21A-B are front and perspective views, respectively, of a firstencoder cylinder embodiment;

FIGS. 22A-B are front and perspective views, respectively, of a secondencoder cylinder embodiment; and

FIGS. 23A-B are front and perspective views, respectively, of a thirdencoder cylinder embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Generally

FIGS. 3-23 illustrate three position-encoder embodiments. Each of theseembodiments advantageously utilize a double-bearing axle to stably mountan optical encoding device for the most precise optical measurements ofthe axle angular position and, hence, the linear position versus time ofa pulser 140 (FIG. 1). In this manner, a precisely measured andcontrolled sensor active pulse can be generated.

FIGS. 3A-B generally illustrate slotted-wheel, position-encoder 301, 302embodiments. The encoders 301, 302 each have an axle 310 with adouble-bearing 320 mount to a housing 330. The slotted wheel 370 ismounted to the axle 310. LEDs 340 illuminate a wheel obverse side anddetectors 350 sense the illumination through wheel slots on a wheelreverse side. A folded, slotted mask 361 is positioned on both sides ofthe slotted wheel 370 so that mask slots align with wheel slots atdiscrete axle positions. Accordingly, axle position pulses are generatedas the axle 310 rotates the wheel 340 and the wheel slots alternatelyblock and pass light, as generated and sensed with the LED/detectoroptics 340, 350.

As shown in FIG. 3A, the LED/detector optics 340, 350 are locatedperpendicular to the slotted wheel, and the mask 361 is reflective. Aslotted wheel position encoder embodiment according to FIG. 3A isdescribed in detail with respect to FIGS. 5-13, below.

As shown in FIG. 3B, the LED/detector optics 340, 350 are locatedparallel to the slotted wheel so as to directly illuminate and sense viathe mask 362. A slotted wheel position encoder embodiment according toFIG. 3B is described in detail with respect to FIGS. 14-17, below.

FIG. 4 generally illustrates a reflective-cylinder, position-encoder 400embodiment. The encoder 400 has an axle 410 with a double-bearing 420mount to a housing 430. A reflective cylinder 440 is mounted to the axle410. The cylinder surface has a repetitive reflective structure disposedacross the length of the cylinder. A commercial optical encoder 450 islocated over the cylinder so as to sense the reflective structure 440and determine axle position accordingly. In an embodiment, the opticalencoder is a 3-channel reflective incremental encoder available fromAvago Technologies, San Jose, Calif. A reflective cylinder positionencoder embodiment according to FIG. 4 is described in detail withrespect to FIGS. 18-23, below.

Slotted Wheel Encoder—Indirect Illumination Encoder Mask

FIGS. 5-13 illustrate details of a double-bearing, slotted-wheel,position-encoder embodiment utilizing an indirectly-illuminated(indirect) encoder mask. FIGS. 5-6 illustrate the double-bearingposition encoder 500 assembly which reads an encoder wheel 900 via awheel-edge-mounted photo interrupter 610. The encoder wheel 900 is partof an encoder assembly 620. The encoder assembly 620 is advantageouslymounted within an double-bearing encoder housing 1000, 1100. The photointerrupter 610 includes an encoder mask block 700 that houses areflective encoder mask (origami) 800, LEDs 1310 and detectors 1320. TheLEDs 1310 and detectors 1320 are mechanically mounted to, and inelectrical communications with, a flex circuit 1200 that generates LED1310 drive signals and receives and processes detector 1320 signals. Theencoder assembly 620 has a encoder wheel 900 mounted between encoderwheel bushings 626 and shaft bushings 624. The photo interrupter 610 ismounted onto the encoder housing 1000, 1100 over an encoder wheel 900edge.

FIGS. 7A-E illustrate an encoder mask block 700 that houses the flexcircuit-mounted optics 1310, 1320 (FIGS. 13A-B) proximate to the encodermask 800 (FIGS. 8A-D). FIGS. 8A-D illustrate the encoder mask 800, whichdefines an encoder wheel path 810, reflective surfaces 820 and maskslots 830. The encoder mask allows the LEDs/detectors 1310, 1320 (FIG.13B) to read the wheel slots at 0 and 90 electrical degrees. Inparticular, LED 1310 (FIG. 13B) light is reflected off one surface 820through the slots 830 and intermittently through the encoder slots 920as the encoder 900 spins within the wheel path 810. The intermittentlight is reflected off another surface 820 to the detectors 1320 (FIG.13B). FIGS. 9A-D illustrate a slotted encoder wheel 900 constructed as athin, round disk defining a center-mount hole 910, encoder slots 920 andan index slot 930.

FIGS. 10-11 illustrate the encoder front housing 1000 and back housing1100 that advantageously provides a double-bear mount for the encoderassembly 620 (FIGS. 6A-B). Further the housing 1000, 1100 positions thephoto interrupter 610 (FIGS. 6A-B) over the encoder wheel 900 so as todetect the passing encoder slots 920 (FIGS. 9A-D). FIGS. 12-13illustrate the encoder flex circuit assembly 1200 and correspondingoptics 1300 and mask block 700, which generate signals responsive to theencoder 900 (FIGS. 9A-D) position as it rotates in response to ashaft-coupled, motor-driven active pulser 110, 120, 140 (FIG. 1).

Slotted Wheel Encoder—Direct Illumination Mask

FIGS. 14-17 illustrate details of a double-bearing, slotted-wheel,position-encoder 1400 embodiment utilizing a direct illumination encodermask. FIGS. 15A-D illustrate an encoder mask block 1500 that positionsflex circuit-mounted optics to the mask 1600 (FIGS. 16A-D). FIGS. 16A-Dillustrate the encoder mask origami 1600 having mask slots for readingthe wheel slots at 0 and 90 electrical degrees. FIGS. 17A-B illustrateflex circuit optics 1700 and the corresponding encoder mask block 1500(FIGS. 15A-D).

As shown in FIGS. 14A-B, a double-bearing position encoder 1400 assemblyreads an encoder wheel portion of an encoder assembly 1420 via awheel-edge-mounted direct illumination mask 1600 and proximate-mountedLED/detector optics 1700 (FIGS. 17A-B). The encoder assembly 1420 isadvantageously mounted within an double-bearing encoder housing 1401,1402. A photo interrupter includes an encoder mask block 1500 thathouses a direct illumination encoder mask 1600, LEDs 1710 (FIG. 17B) anddetectors 1720 (FIG. 17B). The LEDs and detectors are mechanicallymounted to, and in electrical communications with, a flex circuit 1701that generates LED drive signals and receives and processes detectorsignals. The encoder assembly 1420 has a encoder wheel mounted betweenencoder wheel bushings and shaft bushings as described above. The photointerrupter 1500, 1600 is mounted onto the encoder housing 1401, 1402over an encoder wheel edge.

FIGS. 15A-D illustrate an encoder mask block 1500 that houses the flexcircuit-mounted optics 1710, 1720 (FIGS. 17B) proximate to the encodermask 1600 (FIGS. 16A-D). FIGS. 16A-D illustrate the encoder mask 1600,which defines an encoder wheel path 1610, a direct optical path 1620 andmask slots 1630. The encoder mask allows the LEDs/detectors 1710, 1720(FIG. 17B) to read the wheel slots at 0 and 90 electrical degrees. Inparticular, LED 1710 (FIG. 13B) light is directly transmitted 1620through the slots 1630 and intermittently through the encoder slots 920(FIG. 9B) as the encoder spins within the wheel path 1610. Theintermittent light is directly transmitted 1620 to the detectors 1720(FIG. 17B).

Reflective Cylinder Encoder

FIG. 18-23 illustrate details of double-bearing, reflective cylinder,position-encoder 1800 embodiment utilizing an off-the-shelf reflectiveencoder 1810 mounted proximate a double-bearing reflective encodercylinder 2100-2300 (FIGS. 21-23). FIGS. 18-20 illustrate thedouble-bearing position encoder 1800 embodiment having an off-the-shelfreflective encoder 1810, an encoder block 1820 and a reflective encodercylinder 2100-2300. FIGS. 21-23 illustrate various encoder cylinderembodiments.

A double-bearing position encoder has been disclosed in detail inconnection with various embodiments. These embodiments are disclosed byway of examples only and are not to limit the scope of the claims thatfollow. One of ordinary skill in the art will appreciate many variationsand modifications.

What is claimed is:
 1. A double-bearing position encoder has an axlestabilized within a housing via bearings disposed on opposite walls ofthe housing, the axle is in communications with a rotating cam thatactuates a pulser so as to generate an active pulse at a tissue site foranalysis by an optical sensor, the axle rotates a slotted encoder wheelor a reflective encoder cylinder so as to accurately determine the axleposition and, hence, the active pulse frequency and phase, thedouble-bearing position encoder comprising: a housing; a pair ofbearings disposed within opposite facing walls of the housing; an axledisposed within the housing and supported by the bearings, the axle inmechanical communications with a pulser; an encoder wheel fixedlyattached to the axle and having a plurality of wheel slots; an LEDdisposed within the housing that illuminates the encoder wheel; and adetector responsive to the LED illumination after optical interactionwith the wheel slots as the axle rotates the wheel so as to indicate thewheel position.
 2. The encoder according to claim 1 further comprisingan encoder mask having a plurality of mask slots disposed over an edgeand along both sides of the encoder wheel so that the LED illuminationpasses through the mask slots and the wheel slots before reaching thedetector.
 3. The encoder according to claim 2 wherein the encoder maskis folded so that LED light is reflected off of the mask a first timebefore illuminating the encoder wheel and second time before reachingthe detector.
 4. The encoder according to claim 2 wherein the encodermask is folded so that LED light is not reflected off of the mask beforeilluminating the encoder wheel and before reaching the detector.
 5. Anencoding method for determining the position of a rotatable axlecomprising: rotatably mounting an encoder wheel on adouble-bearing-mounted axle; folding an encoder mask proximate an outeredge of the encoder wheel; disposing a plurality of wheel slots aroundthe encoder wheel proximate the outer edge; disposing a plurality ofmask slots through the encoder mask; and disposing an emitter and adetector proximate to and on either side of the encoder wheel so thatlight intermittently passes through the encoder wheel via the wheelslots and the mask slots.
 6. The encoding method according to claim 5further comprising reflecting light from the emitter off of the mask atleast once before it reaches the detector.
 7. The encoding methodaccording to claim 6 further comprising reflecting light from theemitter off of the mask at least twice before it reaches the detector.8. The encoding method according to claim 5 further comprising directlyilluminating the detector from the emitter without reflection off themask.
 9. An optical encoder that indicates the position of a rotatableaxle comprising: a double bearing means of stabilizing a rotatable axlewithin an encoder housing; an encoder wheel means fixedly mounted to theaxle so as to rotate as the axle rotates; an illumination and detectionmeans of intermittently passing light through the encoder wheel means asit rotates; and a folded and slotted mask means of precisely passinglight through encoder wheel.